Direct drive rotor with metal coupler

ABSTRACT

A rotor for an outer rotor-type motor is provided. The rotor includes a metallic coupler and a polymeric frame molded over at least part of the metallic coupler.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 14/270,083,filed May 5, 2014, which is a continuation of U.S. patent applicationSer. No. 13/916,481, filed Jun. 12, 2013, which is a continuation ofU.S. patent application Ser. No. 13/686,718, filed Nov. 27, 2012, whichis a continuation of U.S. patent application Ser. No. 12/893,816, filedSep. 29, 2010, which claims the benefit of U.S. Provisional ApplicationNo. 61/374,578, filed Aug. 17, 2010, all of which are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

The present invention is generally directed toward the field of electricmotors. More specifically, the present invention is directed to outerrotor-type electric motors. Still more specifically, the presentinvention is directed to rotors of outer rotor-type motors, which tendto be useful for use in direct drive clothes washing machines.

BACKGROUND

Direct drive clothes washing machine motor rotors are directly coupledto the shaft that drives the washing machine to transmit the torqueproduced by the motor. The types of rotors used in these applicationsuntil now fall within in two general categories: plastic rotors andsteel rotors. Each general type is associated with advantages anddisadvantages. For example, steel rotors, although relatively strong anddurable, tend to be relatively heavy and costly. In contrast, plasticrotors tend to be lighter and less costly than steel rotors but becausethe plastic typically used is significantly less strong and durable thanmetal, such rotors must be designed to overcome this factor. Typically,the coupling geometry of a plastic rotor must be adjusted to provide arelatively large area of engagement with the drive shaft. This resultsin a plastic rotor typically having a relatively long axial length,which is not desirable especially for horizontal axis washing machines.Relatively, long axial lengths are not limited to plastic rotors,however, many, if not all, steel rotor designs tend to have relativelyoverall long axial lengths.

In view of the foregoing, a need still exists for a rotor having one ormore of the following characteristics: relatively low cost, relativelyshort in axial length, relatively light weight, relativelystrong/durable coupling with the drive shaft.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a rotor for an outerrotor-type electric motor is provided. The rotor is rotatable about anaxis. The rotor comprises a metallic coupler and a polymeric frameincluding a hub. The metallic coupler includes an inner axial surfaceconfigured to interface with a shaft to be driven by the rotor when themotor is energized, an outer axial surface that corresponds to amultiplicity of outer teeth, and a first generally radial surface. Thehub engages the first generally radial surface. The outer teeth engagethe hub such that torque is transmitted from the coupler to the frame.Each of the outer teeth has a generally arcuate tooth width, W_(tooth),and a radial tooth depth, D_(tooth). Each tooth width W_(tooth) is about62.5% of the corresponding tooth depth D_(tooth).

According to another aspect of the present invention, a rotor for anouter rotor-type electric motor is provided. The rotor is rotatableabout an axis. The rotor comprises a metallic coupler and a polymericframe including a hub. The metallic coupler includes an inner axialsurface configured to interface with a shaft to be driven by the rotorwhen the motor is energized, an outer axial surface that corresponds toa multiplicity of outer teeth, and a first generally radial surface. Thehub engages the first generally radial surface. The outer teeth engagethe hub such that torque is transmitted from the coupler to the frame.The coupler has a nominal outer diameter, OD_(coupler.) Each of theouter teeth has a radial tooth depth, D_(tooth), that is about 5% ofOD_(coupler).

According to another aspect of the present invention, a rotor for anouter rotor-type electric motor is provided. The rotor is rotatableabout an axis. The rotor comprises a metallic coupler and a polymericframe including a hub. The metallic coupler includes an inner axialsurface configured to interface with a shaft to be driven by the rotorwhen the motor is energized, an outer axial surface that corresponds toa multiplicity of outer teeth, and a first generally radial surface. Thehub engages the first generally radial surface. The outer teeth engagethe hub such that torque is transmitted from the coupler to the frame.The coupler has a height, H_(coupler). Each of the outer teeth has aradial tooth depth, D_(tooth), that is from about 5% to about 10% ofH_(coupler).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective drawing of a metal coupler of the presentinvention.

FIG. 2 is a perspective cross-section drawing of a rotor of the presentinvention.

FIG. 3 is a top view of a portion of the metal coupler of the presentinvention, particularly illustrating the preferred outer tooth design.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the present invention is directed to a rotor for anouter rotor-type electric motor. FIGS. 1-3 show various aspects, whichwill be described in greater detail below, of an exemplary embodiment ofthe present invention that is useful as part of an electric motor foroperating a clothes washing machine. To be clear, the directions as setforth herein are in reference to a central axis that would be coaxialwith the axis of a shaft to which the rotor is connected as part of anelectric motor. Additionally, disclosures of typical dimensions are inreference to embodiments in which the present invention is part of amotor used to operate clothes washing machines. The present invention,however, is applicable to other end uses and adjustments to the variousdimensions would be made as appropriate for a particular end use.

Referring to FIG. 2, the rotor 29 has a height, H_(rotor), whichcorresponds to the greatest distance, measured axially, between any twopoints of the rotor, and an outer diameter, OD_(rotor), whichcorresponds to the greatest distance, measured radially, between any twopoints of the rotor. Typically, H_(rotor) is within the range of about180 mm to about 330 mm (about 7 to about 13 inches) and OD_(rotor) iswithin the range of about 50 mm to about 100 mm (about 2 to about 4inches). For example, in the embodiment depicted in FIG. 2, H_(rotor) isabout 65.5 mm (about 2.58 in) and OD_(rotor) is about 290 mm (about11.38 inches).

Metallic Coupler

Referring to FIGS. 1 and 2, the rotor 29 of the present inventioncomprises, among other things, a metallic coupler 10 having a height,H_(coupler), which corresponds to the greatest distance, measuredaxially, between any two points of the coupler, and a nominal outerdiameter, OD_(coupler), which corresponds to the greatest distance,measured radially, between any two points of the coupler. Typically,H_(coupler) is within the range of about 20 to about 40 mm (about 0.75to about 1.5 inches) and OD_(coupler) is within the range of about 25 toabout 50 mm (about 1 to about 2 inches). For example, in the embodimentdepicted in FIG. 1, H_(coupler) is about 28 mm (about 1.10 in) andOD_(coupler) is about 41.5 mm (about 1.63 in). The metallic coupler 10comprises an inner axial surface 11 configured to interface with a shaftto be driven by the rotor when the motor is energized. The configurationof the inner axial surface may be of nearly any configurationappropriate for the application (e.g., the interface between the inneraxial surface and the shaft to be driven is sufficiently secure androbust to withstand and transmit the torque produced by the motor duringits useful lifetime, which may be simulated by subjecting a rotor to7,500 hours at an average elevated wash torque of 25 N-m with a dutycycle of 13 seconds on and 3 seconds off). For example, the shaft mayhave a circular, square, hexagonal, octagonal, or toothed cross-section(i.e., one or more teeth, which may be, for example, splines, knurl,keys, or combinations thereof) and the inner axial surface will besufficiently complimentary thereto. To be clear, a generally triangulartooth that has a knurled surface has straight sides whereas a generallytriangular tooth that has a splined surface has sides that are curved.As depicted in FIG. 1, in one embodiment of the present invention, theinner axial surface 11 comprises a multiplicity of teeth 12, which aresplines.

The metallic coupler 10 further comprises an outer axial surface 13 thatcorresponds to a multiplicity of outer teeth 14. The outer teeth 14 maybe of any configuration (e.g., number, size (e.g., axial length andradial height), shape (e.g., cross-section), spacing (e.g.,circumferential)) that is appropriate for the particular application.More particularly, the foregoing configuration options may be selectedin various combinations such that interface between the outer axialsurface and a polymeric frame (described in greater detail below) issufficiently secure and robust to withstand and transmit the torqueproduce by the motor during its useful lifetime. The outer teeth, forexample, may be selected from the group consisting of knurls, splines,keys, diamond knurls, or combinations thereof. In one embodiment thereare a multiplicity of outer teeth. For example, the number of outerteeth may be at least 10. In another embodiment, the number of outerteeth is least 20 and no more than about 40. In the illustratedembodiment, the outer axial surface 13 comprises a multiplicity ofteeth, in particular 30, that are generally triangular with straightsides, which may be referred to as knurls.

A preferred embodiment of the teeth 14 of the outer axial surface 13 isshown in detail in FIG. 3. Each outer tooth 14 defines a peak 14 a, withthe peaks 14 a cooperatively defining the outer circumference of thecoupler 10. That is, the generally radial distance OD_(teeth) betweenopposed peaks 14 a is equal to OD_(coupler). Thus, in keeping with thepreviously described preferred dimensions of the coupler 10 in general,it is preferred that OD_(teeth is) within the range of about 25 to about50 mm (about 1 to about 2 inches). Most preferably, OD_(teeth) is about41.5 mm (about 1.63 in).

A valley 14 b is defined between each outer tooth 14, with each valley14 b spaced generally radially inwardly from the adjacent peaks 14 a.The most preferred generally radial distance between opposed valleys 14b, or the teeth inner diameter ID_(teeth), is about 37.5 mm (about 1.48in). Thus, in keeping with the most preferred OD_(teeth) of about 41.5mm (about 1.63 in), it is readily apparent that a most preferred toothdepth D_(tooth) (i.e., the generally radial component of the distancebetween the peaks 14 a and the valleys 14 b associated with a givenouter tooth 14) of about 2 mm (about 0.08 in) is defined.

It is also readily apparent from the above most preferred dimensionsthat, in the illustrated embodiment in which thirty (30) outer teeth 14are provided, a most preferred generally arcuate peak-to-peak spacingS_(peaks) of about 1.38 mm (about 0.05 in) is defined between eachadjacent pair of peaks 14 a. A generally arcuate valley-to-valleyspacing, S_(valleys), which may alternatively be referred to as thetooth width, W_(tooth), of about 1.25 mm (about 0.05 in) is also definedbetween each adjacent pair of valleys 14 b or, alternatively, across thebase of each tooth 14.

Thus, the coupler 10 of the present invention may have one or more ofthe following relative dimensional characteristics:

-   -   W_(tooth) is most preferably about 62.5% of D_(tooth);    -   D_(tooth) is most preferably abut 5% of OD_(teeth) (or        OD_(coupler));    -   D^(tooth) may be from about 5% to about 10% of H_(coupler) and        is most preferably about 7.14% of H_(coupler); and    -   S_(valleys) is most preferably about 90.4% of S_(peaks).

The metallic coupler 10 may further comprise one or more annularshoulders 15 radially inward of, and axially outward of each axial endof the outer axial surface 13 and wherein a hub 21 (see below for more adetailed description) is additionally molded over at least one of saidannular shoulders 15 such that it is generally flush with axiallyoutermost exterior surfaces 16 of the metallic coupler.

Polymeric Frame

The rotor of the present invention further comprises a polymeric frame20 that comprises a hub 21 molded over at least the outer axial surfaceof the metal coupler 13. The hub has an outer diameter, OD_(hub), thatis essentially the same as the nominal outer diameter of the couple,OD_(coupler). The polymeric frame further comprises a base 22 that isintegrally formed with the hub 21 and extending radially outwardtherefrom. The base has a thickness, T_(base), which corresponds to thegreatest distance, measured axially, between any two points on theopposite sides of the base. The polymeric frames further comprise a sidewall 23 that is integrally formed with the base 22, wherein the sidewallhas a thickness, T_(sidewall). Typically, T_(base) is within the rangeof about 1.3 to about 3.5 mm (about 0.05 to about 0.14 in). For theembodiment depicted in FIG. 2, T_(base) is about 2.5 mm (about 0.10 in).The polymeric frame also comprises a multiplicity of magnet spacers 24each of which is integrally formed with the side wall 23. The polymericframe may be formed from any polymer appropriate for the application.That said, it is typically desirable to use the lowest cost materialthat has sufficient physical characteristics. For example, the polymericframe may be formed from a filled or nonfilled polymer, wherein thepolymer is linear, branched, or crosslinked, and is selected from thegroup consisting of polyester, polyethylene, polypropylene, polyamide,and copolymers thereof. In one embodiment of the present invention thepolymer is polypropylene.

The base 22 of the polymeric frame 20 may comprise a one or moreopenings 25, which may provide benefits such as reduced weight andenhanced cooling. In one embodiment of the present invention thepolymeric frame further comprises a multiplicity of openings 25. Morespecifically, the openings have a total surface area that is within arange that is from about 10% to about 30% of the nominal surface area ofthe base. More typically, the openings have a total surface area that iswithin a range that is from about 10% to about 20% of the nominalsurface area of the base. For example, the embodiment depicted in FIG. 2has a base with a nominal surface area of about 54,220 mm2 (about 84in2) and the openings constitute about 8,880 mm2 (about 13.75 in2),which is about 16% of the nominal surface area.

Reinforcement Ribs

The polymeric frame may comprise a multiplicity of reinforcement ribs26,27, 28 each of which integrally formed with at least the base. In thedepicted embodiment of the present invention each reinforcement rib hasa thickness, T_(rib), that is about equal to T_(base).

Spacer Ribs

One or more of said reinforcement ribs may be integrally formed with amagnets spacer and extend therefrom 26. These ribs may also extend tothe hub and be integrally formed therewith. In the depicted embodimentthe number of these “spacer ribs” corresponds to the number of magnetspacers.

Concentric Ribs

One or more of said reinforcement ribs may be concentric with the hub27. Further one or more reinforcement ribs 28 may extend from and beintegrally formed with one or more of said concentric ribs.

Backing Ring

The rotor of the present invention further comprises a backing ring 30having a thickness, T_(br), and a height, H_(br), of a magnetic materialmolded over by the polymeric frame 20 and having an outer axial surface31 in contact with the sidewall 23 of the polymeric frame 20. Typically,T_(br) is within the range of about 1.0 to about 5.0 mm (about 0.04 toabout 0.20 in) and H_(br) within the range of about 30 to about 45 mm(about 1.18 to about 1.17 in). In the embodiment depicted in FIG. 2,T_(br) is about 2.8 mm (about 0.11 in) and H_(br) is about 36.5 mm(about 1.43 in). The backing ring may be of any appropriate material(e.g., electrical grade steels, high carbon steels, or combinationsthereof) and appropriate configuration (discrete pieces of magneticmaterial in contact with adjacent pieces to form a ring or amultiplicity of layers formed into a ring) for the application. In thedepicted embodiment of the present invention a multiplicity of layers ofelectrical grade steel.

Magnets

The rotor of the present invention further comprises a multiplicity ofpermanent magnets 40 having a thickness, T_(magnet), and a height,H_(magnet), in contact with an inner axial surface 32 of the backingring 30 and molded over by the polymeric frame 20 and spaced apart bythe magnet spacers 24 of the polymeric frame 20. The magnets may be anyappropriate material such as ferrite magnets. Typically, T_(magnet) iswithin the range of about 5.0 to about 15.0 mm (about 0.20 to about 0.60in) and H_(magnet) within the range of about 30 to about 45 mm (about1.18 to about 1.77 in). In the embodiment depicted in FIG. 2, T_(magnet)is about 6.4 mm (about 0.25 in) and H_(magnet) is about 36.5 mm (about1.43 in).

Rotor Dimensions

The foregoing aspects of the rotor of present invention allow for thedesign and production of rotors that are able to operate in the clotheswashing machines having one or more desirable characteristics such asrelatively low cost, relatively short in axial length (especially inview of the ability to have a relatively large diameter), relativelylight weight, relatively strong/durable coupling with the drive shaft.More particularly, the present invention may be used to produce a for arotor to have one or more of the following characteristics:

-   -   T_(br) may be about equal to T_(sidewall) and H_(br) may be        about equal to T_(magnet);    -   H_(magnet) may be at least about 50% of the H_(rotor);    -   H_(magnet) may be at least about 55% of the H_(rotor);    -   H_(coupler) may be no more than about 45% of H_(rotor);    -   H_(coupler) may be no more than about 40% of H_(rotor);    -   OD_(coupler) may be no more than about 20% of OD_(rotor);    -   OD_(coupler) may be no more than about 15% of OD_(rotor);    -   OD_(hub) may be less than about 30% of OD_(rotor);    -   OD_(hub) may be less than about 20% of OD_(rotor);    -   T_(base) and T_(sidewall) may each be less than T_(magnet); and    -   T_(base) and T_(sidewall) may each be about less than 70% of        T_(magnet).

EXAMPLE

A rotor in accordance with that depicted in FIGS. 1-3 and described indetail above was tested by applying about 40 N-m of torque via a shaftonto which the rotor is installed. In comparison, a rotor with ametallic coupler essentially identical to that of the depictedembodiment except for instead of having other teeth, the metalliccoupler has an outer surface that is octagonal. The rotor depicted inthe figures having the toothed metallic coupler withstood theapplication of torque with no visible damage. In contrast, the rotorwith octagonal insert was damaged at the interface between the couplerand the hub and the octagonal insert began to rotate within the hub.Finite element analysis of the two rotors showed that plastic hub of therotor with the octagonal insert saw a maximum stress of about 47.75 MPawhereas the hub of the rotor with the splined metallic insert saw amaximum stress of about 7.25 MPa. Thus, utilizing the splined metallicinsert reduced the stress to the plastic hub by about 85%.

As various modifications could be made in the constructions and methodsherein described and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. Thus, the breadth and scope of thepresent invention should not be limited by the above-described exemplaryembodiment, but should be defined only in accordance with the followingclaims appended hereto and their equivalents.

It should also be understood that when introducing elements of thepresent invention in the claims or in the above description of exemplaryembodiments of the invention, the terms “comprising,” “including,” and“having” are intended to be open-ended and mean that there may beadditional elements other than the listed elements. Additionally, theterm “portion” should be construed as meaning some or all of the item orelement that it qualifies. Moreover, use of identifiers such as first,second, and third should not be construed in a manner imposing anyrelative position or time sequence between limitations.

1. A rotor for an outer rotor-type electric motor, said rotor beingrotatable about an axis, the rotor comprising: a metallic couplerincluding an inner axial surface configured to interface with a shaft tobe driven by the rotor when the motor is energized, an outer axialsurface that corresponds to a multiplicity of outer teeth, and a firstgenerally radial surface; and a polymeric frame including a hub, saidhub engaging the first generally radial surface, said outer teethengaging the hub such that torque is transmitted from the coupler to theframe, each of said outer teeth having a generally arcuate tooth width,W_(tooth), and a generally radial tooth depth, D_(tooth), each toothwidth W_(tooth) being about 62% of the corresponding tooth depthD_(tooth).